The invention relates to a method for controlling the radiation pattern of an antenna means comprising N helically configured radiating elements, where N is an integer greater than 1, and being adapted for transmitting and/or receiving RF signals. It also relates to an antenna system for transmission/reception of RF signals, comprising N helically configured antenna elements, where N is an integer greater than 1, and being adapted for transmitting and/or receiving RF signals. The invention further relates to a radio communication device including such an antenna system.
For antenna applications where a hemispherical coverage with circular polarization is desired, a quadrifilar helix antenna (QHA) can be used. An advantage of the QHA is the ability to shape the radiation pattern from a narrow axial beam to a very broad beam covering almost the entire sphere. The pattern can also be designed to have peaks and dips at certain angles. This is done by exciting different radiation modes, axial and/or radial ones.
A QHA consists of four wires wound around a cylindrical or conical surface with a constant pitch angle. Usually, when space is limited, the choice is a narrow and short cylindrical QHA, having three degrees of freedom (e.g. diameter, pitch angle, length). Allowing the surface to be conical gives one extra degree of freedom, and can significantly increase the bandwidth.
Modifications can be added to the helices to achieve certain features. Each helix can for example be split in two, the halves having different lengths, for double tuning. Also, if the circumference is large enough, the helices can be meandered to reduce the length of the antenna. A QHA is fed at either the bottom or the top end by means of a feed network.
Several quadrifilar helix antennas (QHA), are known from patents and published patent applications. A large number of these disclose quadrifilar antenna structures for circularly polarized radio signals. See, for example, WO 98/28815, WO 97/06579, WO 97/11507, U.S. Pat. No. 5,191,352, U.S. Pat. No. 5,255,005, and U.S. Pat. No. 5,541,617.
In all those antenna structures, helical elements are fed with constant amplitude and constant phase-shift between the helical elements. FIG. 1 shows a typical radiation pattern of such an antenna structure mounted to a portable radio-telephone. The radiation pattern exhibits a main lobe M directed upwards and, in most cases, a minor back lobe B directed downwards when fed with a progressive phase-shift adapted to the rotational directions of the helical elements. Between the lobes, the radiation pattern has a blind sector or null BS, where reception/transmission cannot be performed.
In order to direct the main antenna lobe towards a transmitter/receiver (e.g. a satellite) with which a radio communication device is to communicate, telephones having an antenna structure mounted to the telephone housing with a pivot joint have for example been provided. The orientation of the antenna structure can then be adjusted manually for good signal transmission/reception. New adjustments can take place when the transmitter/receiver has changed location or when the telephone has been moved. An example of an antenna structure mounted with a pivoting joint to a telephone is disclosed in U.S. Pat. No. 5,628,057.
In this disclosure it is to be understood that the antenna system of the invention is operable to receive or receive and transmit radio signals. Even if a term is used herein that suggests one specific signal direction it is to be appreciated that such a situation can cover that signal direction and/or its reverse.
A main object of the invention is to provide a method for controlling the radiation pattern of an antenna means comprising N helically configured radiating elements (NHA), in response to signals received.
Another object of the invention is to provide a method for controlling the radiation pattern of an antenna means comprising N helically configured radiating elements (NHA), by which method blind sectors in the radiation pattern can be avoided.
A further object of the invention is to provide a method for controlling the radiation pattern of an antenna means comprising N helically configured radiating elements (NHA), by which method the radiation pattern can be adapted to optimal reception/transmission.
These and other objects are attained by a method according to the appended method claims.
The invention further provides a method for controlling the radiation pattern of an antenna means comprising N helically configured radiating elements (NHA), by which method the radiation pattern can be controlled during reception and/or transmission.
The invention further provides a method for controlling the radiation pattern of an antenna means comprising N helically configured radiating elements (NHA), by which method the sensitivity to antenna orientation and transmitter/receiver position can be reduced.
The invention further provides a method for controlling the radiation pattern of an antenna means comprising N helically configured radiating elements (NHA), by which method the performance of the antenna means in stowed position can be improved.
The invention further provides a method for controlling the radiation pattern of an antenna means comprising N helically configured radiating elements (NHA), by which method the average signal and signal-to-noise ratio can be improved.
The invention further provides a method for controlling the radiation pattern of an antenna means comprising N helically configured radiating elements (NHA), by which method the sensitivity to mechanical tolerances in the antenna means can be reduced.
A further main object of the invention is to provide an antenna system comprising N helically configured antenna elements, with which antenna system the radiation pattern can be controlled.
Another object of the invention is to provide an antenna system, with which blind sectors in the radiation pattern can be avoided.
Another object of the invention is to provide an antenna system, with which the radiation pattern can be adapted to optimal reception/transmission.
These and other objects are attained by an antenna system according to the appended system claims.
The invention further provides an antenna system, by which the radiation pattern can be controlled during reception and/or transmission.
The invention further provides an antenna system, in which the sensitivity to antenna orientation and transmitter/receiver position can be reduced.
The invention further provides an antenna system, by which the performance of the antenna system with the radiating elements in stowed position can be improved.
The invention further provides an antenna system, by which the average signal and signal-to-noise ratio can be improved.
The invention further provides an antenna system, in which the sensitivity to mechanical tolerances can be reduced.
A further main object of the invention is to provide a radio communication device having an antenna system with the above mentioned objects.
These and other objects are attained by a radio communication device according to the appended claims concerning a radio communication device.